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Article: Incidence of the Brownian Relaxation Process on the Magnetic Properties of Ferrofluids.

Vajtai, Lili / Nemes, Norbert Marcel / Morales, Maria Del Puerto / Molnár, Kolos / Pinke, Balázs Gábor / Simon, Ferenc

2024 Volume 14, Issue 7

Abstract: Ferrofluids containing magnetic nanoparticles represent a special class of magnetic materials due to the added freedom of particle tumbling in the fluids. We studied this process, known as Brownian relaxation, and its effect on the magnetic properties of ...

Abstract	Ferrofluids containing magnetic nanoparticles represent a special class of magnetic materials due to the added freedom of particle tumbling in the fluids. We studied this process, known as Brownian relaxation, and its effect on the magnetic properties of ferrofluids with controlled magnetite nanoparticle sizes. For small nanoparticles (below 10 nm diameter), the Néel process is expected to dominate the magnetic response, whereas for larger particles, Brownian relaxation becomes important. Temperature- and magnetic-field-dependent magnetization studies, differential scanning calorimetry, and AC susceptibility measurements were carried out for 6 and 13.5 nm diameter magnetite nanoparticles suspended in water. We identify clear fingerprints of Brownian relaxation for the sample of large-diameter nanoparticles as both magnetic and thermal hysteresis develop at the water freezing temperature, whereas the samples of small-diameter nanoparticles remain hysteresis-free down to the magnetic blocking temperature. This is supported by the temperature-dependent AC susceptibility measurements: above 273 K, the data show a low-frequency Debye peak, which is characteristic of Brownian relaxation. This peak vanishes below 273 K.
Language	English
Publishing date	2024-04-05
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2662255-5
ISSN	2079-4991
ISSN	2079-4991
DOI	10.3390/nano14070634
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Article: Formation of Paramagnetic Defects in the Synthesis of Silicon Carbide.

Mukesh, Nain / Márkus, Bence G / Jegenyes, Nikoletta / Bortel, Gábor / Bezerra, Sarah M / Simon, Ferenc / Beke, David / Gali, Adam

Micromachines

2023 Volume 14, Issue 8

Abstract: Silicon carbide (SiC) is a very promising platform for quantum information processing, as it can host room temperature solid state defect quantum bits. These room temperature quantum bits are realized by paramagnetic silicon vacancy and divacancy defects ...

Abstract	Silicon carbide (SiC) is a very promising platform for quantum information processing, as it can host room temperature solid state defect quantum bits. These room temperature quantum bits are realized by paramagnetic silicon vacancy and divacancy defects in SiC that are typically introduced by irradiation techniques. However, irradiation techniques often introduce unwanted defects near the target quantum bit defects that can be detrimental for the operation of quantum bits. Here, we demonstrate that by adding aluminum precursor to the silicon and carbon sources, quantum bit defects are created in the synthesis of SiC without any post treatments. We optimized the synthesis parameters to maximize the paramagnetic defect concentrations-including already established defect quantum bits-monitored by electron spin resonance spectroscopy.
Language	English
Publishing date	2023-07-28
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2620864-7
ISSN	2072-666X
ISSN	2072-666X
DOI	10.3390/mi14081517
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Article ; Online: DNA mismatch repair protects the genome from oxygen-induced replicative mutagenesis.

Lózsa, Rita / Németh, Eszter / Gervai, Judit Z / Márkus, Bence G / Kollarics, Sándor / Gyüre, Zsolt / Tóth, Judit / Simon, Ferenc / Szüts, Dávid

Nucleic acids research

2023 Volume 51, Issue 20, Page(s) 11040–11055

Abstract: DNA mismatch repair (MMR) corrects mismatched DNA bases arising from multiple sources including polymerase errors and base damage. By detecting spontaneous mutagenesis using whole genome sequencing of cultured MMR deficient human cell lines, we show that ...

Abstract	DNA mismatch repair (MMR) corrects mismatched DNA bases arising from multiple sources including polymerase errors and base damage. By detecting spontaneous mutagenesis using whole genome sequencing of cultured MMR deficient human cell lines, we show that a primary role of MMR is the repair of oxygen-induced mismatches. We found an approximately twofold higher mutation rate in MSH6 deficient DLD-1 cells or MHL1 deficient HCT116 cells exposed to atmospheric conditions as opposed to mild hypoxia, which correlated with oxidant levels measured using electron paramagnetic resonance spectroscopy. The oxygen-induced mutations were dominated by T to C base substitutions and single T deletions found primarily on the lagging strand. A broad sequence context preference, dependence on replication timing and a lack of transcriptional strand bias further suggested that oxygen-induced mutations arise from polymerase errors rather than oxidative base damage. We defined separate low and high oxygen-specific MMR deficiency mutation signatures common to the two cell lines and showed that the effect of oxygen is observable in MMR deficient cancer genomes, where it best correlates with the contribution of mutation signature SBS21. Our results imply that MMR corrects oxygen-induced genomic mismatches introduced by a replicative process in proliferating cells.
MeSH term(s)	Humans ; Base Pair Mismatch ; DNA Mismatch Repair ; DNA Repair ; DNA Replication ; Mutagenesis ; Mutation ; Oxygen ; Cell Line
Chemical Substances	Oxygen (S88TT14065)
Language	English
Publishing date	2023-10-04
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	186809-3
ISSN	1362-4962 ; 1362-4954 ; 0301-5610 ; 0305-1048
ISSN (online)	1362-4962 ; 1362-4954
ISSN	0301-5610 ; 0305-1048
DOI	10.1093/nar/gkad775
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Article ; Online: Unusual spin dynamics in topological insulators.

Dóra, Balázs / Simon, Ferenc

Scientific reports

2015 Volume 5, Page(s) 14844

Abstract: The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form around the Zeeman energy in conventional materials with weak spin orbit coupling, whose spectral width characterizes the spin relaxation rate. We show that DSS has an unusual non- ... ...

Abstract	The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form around the Zeeman energy in conventional materials with weak spin orbit coupling, whose spectral width characterizes the spin relaxation rate. We show that DSS has an unusual non-Lorentzian form in topological insulators, which are characterized by strong SOC, and the anisotropy of the DSS reveals the orientation of the underlying spin texture of topological states. At zero temperature, the high frequency part of DSS is universal and increases in certain directions as ω(d-1) with d = 2 and 3 for surface states and Weyl semimetals, respectively, while for helical edge states, the interactions renormalize the exponent as d = 2K - 1 with K the Luttinger-liquid parameter. As a result, spin relaxation rate cannot be deduced from the DSS in contrast to the case of usual metals, which follows from the strongly entangled spin and charge degrees of freedom in these systems.
Language	English
Publishing date	2015-10-06
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/srep14844
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Article: Studying single-wall carbon nanotubes through encapsulation: from optical methods till magnetic resonance.

Simon, Ferenc

Journal of nanoscience and nanotechnology

2006 Volume 7, Issue 4-5, Page(s) 1197–1220

Abstract: Encapsulating fullerenes, magnetic fullerenes, 13C isotope enriched fullerenes, and organic solvents inside SWCNTs enables to yield unprecedented insight into their electronic, optical, and interfacial properties and to study SWCNT growth. In addition to ...

Abstract	Encapsulating fullerenes, magnetic fullerenes, 13C isotope enriched fullerenes, and organic solvents inside SWCNTs enables to yield unprecedented insight into their electronic, optical, and interfacial properties and to study SWCNT growth. In addition to customary methods of their studies such as e.g., optical absorption or Raman spectroscopy, these efforts enables to employ electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopy. Encapsulated C60 fullerenes are transformed to inner tubes by a high temperature annealing. The diameter distribution of the inner tubes follow that of the outer ones and their unique, low defect concentration makes them an ideal model system for high resolution and energy dependent Raman studies. The observation of Raman modes of individual inner-outer tube pairs allows to measure the inner-outer tube interaction strength that is also well described theoretically. Reversible closing and opening of SWCNT can be studied in a diameter selective manner by encapsulating C60 and transforming it to an inner tube. The growth of inner tubes can be achieved from 13C enriched encapsulated organic solvents, which shows that the geometry of the fullerene does not play a particular role in the inner tube growth as it was originally thought. In addition, it opens new perspectives to explore the in-the-tube chemistry. Growth of inner tubes from 13C enriched fullerenes provides a unique isotope engineered heteronuclear system, where the outer tubes contain natural carbon and the inner walls are controllably 13C isotope enriched. The material enables to identify the vibrational modes of inner tubes which otherwise strongly overlap with the outer tube modes. The 13C NMR signal of the material has an unprecedented specificity for the small diameter SWCNTs. Temperature and field dependent 13C T1 studies show a uniform metallic-like electronic state for all inner tubes rather than distributed metallic and isolating behavior. A low energy, 3 meV gap is observed that is tentatively assigned to a long sought Peierls transition in the small diameter SWCNTs. Encapsulating magnetic fullerenes, such as N@C60 and C59N opens the way for local probe ESR studies of the electronic properties of the SWCNTs.
MeSH term(s)	Carbon/chemistry ; Electron Spin Resonance Spectroscopy/methods ; Electrons ; Fullerenes/chemistry ; Isotopes ; Magnetic Resonance Spectroscopy/methods ; Microscopy, Electron, Transmission ; Models, Statistical ; Nanotechnology/methods ; Nanotubes, Carbon/chemistry ; Nitrogen/chemistry ; Solvents/chemistry ; Spectrum Analysis, Raman ; Temperature
Chemical Substances	Fullerenes ; Isotopes ; Nanotubes, Carbon ; Solvents ; Carbon (7440-44-0) ; Nitrogen (N762921K75) ; fullerene C60 (NP9U26B839)
Language	English
Publishing date	2006-01-30
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't ; Review
ISSN	1533-4880
ISSN	1533-4880
DOI	10.1166/jnn.2007.306
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Article ; Online: Spin-relaxation time in materials with broken inversion symmetry and large spin-orbit coupling.

Szolnoki, Lénárd / Kiss, Annamária / Dóra, Balázs / Simon, Ferenc

Scientific reports

2017 Volume 7, Issue 1, Page(s) 9949

Abstract: We study the spin-relaxation time in materials where a large spin-orbit coupling (SOC) is present which breaks the spatial inversion symmetry. Such a spin-orbit coupling is realized in zincblende structures and heterostructures with a transversal ... ...

Abstract	We study the spin-relaxation time in materials where a large spin-orbit coupling (SOC) is present which breaks the spatial inversion symmetry. Such a spin-orbit coupling is realized in zincblende structures and heterostructures with a transversal electric field and the spin relaxation is usually described by the so-called D'yakonov-Perel' (DP) mechanism. We combine a Monte Carlo method and diagrammatic calculation based approaches in our study; the former tracks the time evolution of electron spins in a quasiparticle dynamics simulation in the presence of the built-in spin-orbit magnetic fields and the latter builds on the spin-diffusion propagator by Burkov and Balents. Remarkably, we find a parameter free quantitative agreement between the two approaches and it also returns the conventional result of the DP mechanism in the appropriate limit. We discuss the full phase space of spin relaxation as a function of SOC strength, its distribution, and the magnitude of the momentum relaxation rate. This allows us to identify two novel spin-relaxation regimes; where spin relaxation is strongly non-exponential and the spin relaxation equals the momentum relaxation. A compelling analogy between the spin-relaxation theory and the NMR motional narrowing is highlighted.
Language	English
Publishing date	2017-08-30
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/s41598-017-09759-0
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Article ; Online: The Elliott-Yafet theory of spin relaxation generalized for large spin-orbit coupling.

Kiss, Annamária / Szolnoki, Lénard / Simon, Ferenc

Scientific reports

2016 Volume 6, Page(s) 22706

Abstract: We generalize the Elliott-Yafet (EY) theory of spin relaxation in metals with inversion symmetry for the case of large spin-orbit coupling (SOC). The EY theory treats the SOC to the lowest order but this approach breaks down for metals of heavy elements ( ...

Abstract	We generalize the Elliott-Yafet (EY) theory of spin relaxation in metals with inversion symmetry for the case of large spin-orbit coupling (SOC). The EY theory treats the SOC to the lowest order but this approach breaks down for metals of heavy elements (such as e.g. caesium or gold), where the SOC energy is comparable to the relevant band-band separation energies. The generalized theory is presented for a four-band model system without band dispersion, where analytic formulae are attainable for arbitrary SOC for the relation between the momentum- and spin-relaxation rates. As an extended description, we also consider an empirical pseudopotential approximation where SOC is deduced from the band potential (apart from an empirical scaling constant) and the spin-relaxation rate can be obtained numerically. Both approaches recover the usual EY theory for weak SOC and give that the spin-relaxation rate approaches the momentum-relaxation rate in the limit of strong SOC. We argue that this limit is realized in gold by analyzing spin relaxation data. A calculation of the g-factor shows that the empirical Elliott-relation, which links the g-factor and spin-relaxation rate, is retained even for strong SOC.
Language	English
Publishing date	2016-03-04
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/srep22706
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Article ; Online: Room-Temperature Defect Qubits in Ultrasmall Nanocrystals.

Beke, Dávid / Valenta, Jan / Károlyházy, Gyula / Lenk, Sándor / Czigány, Zsolt / Márkus, Bence Gábor / Kamarás, Katalin / Simon, Ferenc / Gali, Adam

The journal of physical chemistry letters

2020 Volume 11, Issue 5, Page(s) 1675–1681

Abstract: There is an urgent quest for room-temperature qubits in nanometer-sized, ultrasmall nanocrystals for quantum biosensing, hyperpolarization of biomolecules, and quantum information processing. Thus far, the preparation of such qubits at the nanoscale has ... ...

Abstract	There is an urgent quest for room-temperature qubits in nanometer-sized, ultrasmall nanocrystals for quantum biosensing, hyperpolarization of biomolecules, and quantum information processing. Thus far, the preparation of such qubits at the nanoscale has remained futile. Here, we present a synthesis method that avoids any interaction of the solid with high-energy particles and uses self-propagated high-temperature synthesis with a subsequent electrochemical method, the no-photon exciton generation chemistry to produce room-temperature qubits in ultrasmall nanocrystals of sizes down to 3 nm with high yield. We first create the host silicon carbide (SiC) crystallites by high-temperature synthesis and then apply wet chemical etching, which results in ultrasmall SiC nanocrystals and facilitates the creation of thermally stable defect qubits in the material. We demonstrate room-temperature optically detected magnetic resonance signal of divacancy qubits with 3.5% contrast from these nanoparticles with emission wavelengths falling in the second biological window (1000-1380 nm). These results constitute the formation of nonperturbative bioagents for quantum sensing and efficient hyperpolarization.
Language	English
Publishing date	2020-02-14
Publishing country	United States
Document type	Journal Article
ISSN	1948-7185
ISSN (online)	1948-7185
DOI	10.1021/acs.jpclett.0c00052
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Article: Unusual hyperfine interaction of dirac electrons and NMR spectroscopy in graphene.

Dóra, Balázs / Simon, Ferenc

Physical review letters

2009 Volume 102, Issue 19, Page(s) 197602

Abstract: A theory of nuclear magnetic resonance (NMR) in graphene is presented. The canonical form of the electron-nucleus hyperfine interaction is strongly modified by the linear electronic dispersion. The NMR shift and spin-lattice relaxation time are ... ...

Abstract	A theory of nuclear magnetic resonance (NMR) in graphene is presented. The canonical form of the electron-nucleus hyperfine interaction is strongly modified by the linear electronic dispersion. The NMR shift and spin-lattice relaxation time are calculated as a function of temperature, chemical potential, and magnetic field, and three distinct regimes are identified: Fermi-, Dirac-gas, and extreme quantum limit behaviors. A critical spectrometer assessment shows that NMR is within reach for fully 13C enriched graphene of reasonable size.
Language	English
Publishing date	2009-05-15
Publishing country	United States
Document type	Journal Article
ZDB-ID	208853-8
ISSN	1079-7114 ; 0031-9007
ISSN (online)	1079-7114
ISSN	0031-9007
DOI	10.1103/PhysRevLett.102.197602
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Article: Electron-spin dynamics in strongly correlated metals.

Dóra, Balázs / Simon, Ferenc

Physical review letters

2009 Volume 102, Issue 13, Page(s) 137001

Abstract: The temperature dependence of the electron-spin lifetime T1 and the g factor are anomalous in alkali fullerides (K,Rb)3C60, which cannot be explained by the canonical Elliott-Yafet theory. These materials are archetypes of strongly correlated and narrow ... ...

Abstract	The temperature dependence of the electron-spin lifetime T1 and the g factor are anomalous in alkali fullerides (K,Rb)3C60, which cannot be explained by the canonical Elliott-Yafet theory. These materials are archetypes of strongly correlated and narrow band metals. We introduce the concept of a "complex electron-spin resonance frequency shift" to treat these measurables in a unified manner within the Kubo formalism. The theory is applicable for metals with nearly degenerate conduction bands and large momentum scattering even with an anomalous temperature dependence and sizable residual value.
Language	English
Publishing date	2009-04-03
Publishing country	United States
Document type	Journal Article
ZDB-ID	208853-8
ISSN	1079-7114 ; 0031-9007
ISSN (online)	1079-7114
ISSN	0031-9007
DOI	10.1103/PhysRevLett.102.137001
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